That's not how LTIR works.
players on LTIR never come off the books, his cap hit already counts in full against them. Right now they have access to LTIR relief. Any players added to the roster after they place Pacioretty on LTIR have used that relief pool rather than added to their cumulative cap hit.
Carolina's ACLS is 82.486 mil, they didn't have much room when Pacietty went on LTIR. they have 11 mil in LTIR salary pool from Pacioretty and Gardiner. When Pacietty comes off, they will only have ~4 mil in LTIR relief left max from Gardiner, and will be right tight to their limit as their roster can not exceed the ACLS + their LTIR relief. Right now their roster has a cap hit of about 86.5 mil, so when Pacioretty comes back they will be right up against their max unless the make a move, but moving Stepan Drury or Noesen will give them some space.
Like I said, they are really tight, any callups from injuries along the way could make it even tighter.